Enhanced Hydrodeoxygenation of Guaiacol to Phenol over MgO-Supported Pt Catalysts: The Critical Role of Sodium Promotion

The modulation of catalyst surfaces with alkali metals is a key research topic in heterogeneous catalysis. This study elucidates the mechanistic role of sodium promotion in enhancing the performance of MgO-supported Pt catalysts for the selective hydrodeoxygenation (HDO) of guaiacol to phenol. The catalytic activity exhibited a distinct volcano-shaped trend as a function of sodium content, with optimal performance achieved using the Pt-5Na/MgO catalyst. Under the conditions of 280 °C and 0.1 MPa H2 pressure, the Pt-5Na/MgO catalyst achieved 98% conversion and 91% phenol selectivity. Mechanistic studies revealed that sodium modification increased the basicity of the support, and a correlation was observed between guaiacol conversion and the density of surface basic sites. Additionally, sodium addition induced electronic restructuring of the catalyst by transferring electrons from Na to Pt, which increased the electron density of Pt nanoparticles, facilitated the reduction of Pt, and generated more catalytically active Pt species. This electronic modification enhanced the hydrogen activation capacity of Pt species, while the stabilization of hydrogen species on basic sites enhanced hydrogen spillover efficiency, thereby increasing the availability of reactive hydrogen species. The findings provide insight into the design of alkali-metal-promoted Pt catalysts for hydrogenation applications.